Fuel system

ABSTRACT

A fuel system for an internal combustion engine employs fluid logic devices for controlling a fuel injector valve. The fuel requirement is delivered in intermittent pulses having variable time duration as necessary to meet changes in the fuel requirement. Fluid logic devices provide a control signal for operating the fuel injector valve in the form of a train of pulses having a repetition rate N and pulse width of Q/N where N is a function of engine speed and Q is a function of the flow rate of air inducted into the engine. Thus the train of pulses provides a control signal related to N X (Q/N) Q which is desirable for maintaining a selected air-fuel ratio. The logic circuitry includes a variable pulse width multivibrator having an external bias connection providing an output signal in the form of a train of pulses having a repetition rate corresponding to a first input signal and a pulse width related to the reciprocal of the bias signal pressure.

trite States atent 1151 3,337,121

Tuzson Aug. 29, 1972 [54] FUEL SYSTEM ABSTRACT [72] Inventor: John J. Tuzson, Evanston, Ill. A fuel system for an internal combustion engine employs fluid logic devices for controlling a fuel injector [73] Asslgnee' Borg'wamer Corporauon Chicago valve. The fuel requirement is delivered in intermittent pulses having variable time duration as necessary [22] Filed; 2 1970 to meet changes in the fuel requirement. Fluid logic devices provide a control signal for operating the fuel PP N05 101,562 injector valve in the form of a train of pulses having a repetition rate N and pulse width of Q/N where N is a 52 US. c1..123/119 R; 123/139 AW, l23/DIG. 10, function of engine speed and Q is a function of the 123/103, 261/DIG. 69

[51] Int. Cl ..F02d 11/08, F02d 3/00, F02n 39/00 flow rate of air inducted into the engine. Thus the train of pulses provides a control signal related to N X 58 Field of Search .123/139 AW DIG. 10 119 R, (Q/N) Q which is desirable for maintaining a 123/103R. 261/1516 261 selected air-fuel ratio. The logic circuitry includes a variable pulse width multivibrator having an external bias connection providing an output signal in the form [56] References Cited of a train of pulses having a repetition rate cor- UNITED STATES PATENTS responding to a first input signal and a pulse width related to the reciprocal of the bias signal pressure. 3,556,063 1/1971 Tuzson ..123/103 5 Claims, 4 wing Figures Primary ExaminerWendell E. Burns Att0meyDona1d W. Banner, William S. McCurry and John W. Butcher V 34 L 35 v 36 A 37 48* JTL 1\ f\ l 44 77 r 51 a1 7 j H/ 83 [A 47 m r l 41 a 49 78 79 1 H I 52 l i L i 5 3 63 L H) 62 l A I 57 j L 58 1 59 26 I X 1 2 22-\ I I9 23 L 1 00 I rum. SYSTEM SUMMARY OF THE INVENTION The present invention relates generally to fuel systems for internal combustion engines and more particularly to a fuel system including fluid logic devices for metering fuel in accordance with the air inducted into the engine.

A principal object of the present invention is to pro vide a fuel system in which the fuel requirement as measured by the air inducted into the engine is delivered in intermittent pulses related to engine speed; another object is to provide fuel injection control means employing fluid logic devices; a further object is to provide a fluid logic device capable of producing an output signal related to the quotient of two input signals; a still further object is to provide a variable pulse width fluidic multivibrator in which the pulse width varies as a function of the reciprocal of a variable external bias pressure; an additional object is to provide a fuel injector pneumatic control signal in the form of a train of pulses having a repetition rate N and a pulse width of Q/N where N is a function of engine speed and Q is a function of the flow rate of air inducted into the engine; other objects and advantages of the invention will become apparent from the following description together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a fuel system according to the present invention;

FIG. 2 is a diagram illustrating wave forms of various pressure signals versus time;

FIG. 3 is a diagram illustrating certain wave forms of FIG. 2 to enlarged scale; and

FIG. 4 is a diagram illustrating the input and output characteristics of a proportional amplifier shown in FIG. El.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawings, a fuel system for an internal combustion engine is illustrated by means of a schematic symbols, the interrelationships of the various portions of the system being described more fully hereinafter.

An engine it) is indicated schematically as including a cam shaft 11, and inlet valve 12, an intake manifold 13, and a venturi 14 arranged in an air induction passage 16 having a throttle plate for regulating the amount of air inducted into the engine.

A fuel nozzle 17 extends into the intake manifold 13 and is connected to a source of fuel including fuel tank 1%, pump 19, metering valve 21 and connecting conduits 22, 23, 24. As indicated schematically, the pump 19 supplies an excess of fuel to fuel valve 21 from tank 18. Fuel valve 21 permits the fuel to return to tank 18 through conduit 23 in the absence of a pressure signal in control port 26, and delivers fuel to nozzle 17 through conduit 24 in response to the presence of a pressure signal in control port 26. In practice, it is contemplated that the fuel source may include a plurality of nozzles 17 and valves 21 supplied by a common fuel conduit where it is desired to deliver fuel adjacent respective inlet valves of a multicylinder engine. Fuel valve 21 may take a variety of forms provided that it possesses the capability of directing fuel to the fuel nozzle in accordance with a pneumatic pressure signal applied to control port 26.

The control signal applied to control port 26 is preferably provided by fluid logic circuitry in the form of a train of pneumatic pulses having a repetition rate related to engine speed and a pulse width or time duration related to the amount of air inducted into the engine. Fuel valve 21 is thus enabled to meter fuel to the engine in accordance with the air inducted for providing a desired air-fuel ratio, however, the fuel is delivered in intermittent pulses related to engine speed for injection in accordance with the opening and closing of an inlet valve.

Turning now to the fluid logic circuitry for providing the control pressure signal, a source of air under pressure 30 provides a source of pneumatic signal energy and is connected by means of conduits 31, 32, 33 34, 35, 36, 37 with a chopper 38, a first fluid switching device 39, a second fluidic switching device 41, and a proportional amplifier 42. For convenience, the circuit may be considered as including a reference signal generating subcircuit including chopper 38, a pneumatic control signal forming module including first fluidic switching device 39, and a bias signal generating subcircuit including second fluidic switching device 41, proportional amplifier 42 and integrating or filter capacitance 76.

Chopper 38 is schematically indicated as having an input port 43 connected to the source of signal energy 30, an output port 44 connected to conduit 46, and a mechanical drive connection 47 coupled to cam shaft ill. Chopper 38 may take a variety of forms and generally includes means for interrupting an input stream of air to provide an output signal in the form of pneumatic pressure pulses having a repetition rate corresponding to the speed of the mechanical drive connection 47. It is desirable to provide an output reference signal in conduit 46 having a sharp rise time as indicated by the square wave form 2a of FIG. 2. In order to provide a reference signal having the desired pressure rise characteristics, it may be desirable to incorporate fluidic gating means in cooperation with the means for interrupting the air stream. The reference signal supplied to conduit 46 is preferably a train of pneumatic pressure pulses having a sharp rise time and a repetition rate determined by engine speed which for convenience is illustrated as a square wave 2a in FIG. 2. This reference signal 2a also appears in branch conduits 48, 49, 51, 52, and 53 for connection with the pulse forming module and bias network.

The control pulse forming module includes first fluidic switching device 39 which is preferably a monostable fluidic gating device having a power nozzle 56, a control port 57, an inhibitor port 58, a first preferred receiver leg 59 and a second alternate receiver leg 61. The control and inhibitor ports are arranged in opposition to each other across an interaction region, the interaction region being provided with geometric bias such that flow from the power nozzle is received in first receiver leg 59 in the absence of a switching pressure signal in the control port. First receiver leg 59 dumps to atmosphere, second receiver leg 61 is connected to the control port 26 of fuel metering valve 21, and power nozzle 56 is connected to the source of pneumatic signal energy 30 by means of conduits 3i, 32, and 35. Control port 57 is connected to branch conduits 49 and 53 for receiving reference signal 2a, while inhibitor port 58 is connected to branch conduits 49 and 52 through a fluid capacitance coupling indicated by the volume 62. Capacitance 62 and resistance 63 modify the pressure rise characteristics of the reference signal to provide an inhibit signal illustrated by the wave form 2b of FIG. 2.

First fluidic switching device 39 is thus connected in a configuration generally referred to in the art as a one-shot multivibrator. By way of brief explanation, the reference signal and inhibit signal 212 are algebraically combined in the interaction region of the device resulting in a net signal represented by the wave form 20 in FIG. 2. Where the switching characteristic of the device is represented by the energy level 64 in FIG. 2, the net signal results in the formation of a train of pulses in second receiver leg 61 as represented by wave form 2d in FIG. 2. The reference signal pressure rise switches flow from receiver leg 59 to receiver leg 61, and the inhibit signal pressure rise being opposite in direction counteracts the reference signal pressure rise after a time delay determined by the difference in rise times, permitting flow to switch back to first receiver leg 59 as a result of the internal bias of the device.

As thus far described, the time duration 66 of an output pulse 2:! in receiver leg 61 is determined by the volume of capacitance 62 and the impedance represented by restriction 63. However, inhibitor port 58 is also connected to a bias conduit 67 for receiving an external bias pressure which can be considered as back loading capacitance 62. resulting in modification of the rise time of inhibit signal 2b. This change in rise time results in variation of the pulse width or time duration of pulse 2d in receiver 61.

Modification of the pressure rise characteristics of the inhibit signal is shown more clearly in the larger scale wave forms of FIG. 3. A high bias pressure results in a rapid pressure rise in the inhibit signal as indicated by 68, an intermediate bias pressure results in an intermediate pressure rise rate as indicated by 69, and a low bias pressure results in a slow pressure rise as indicated by 7 1 Where the switching pressure level of the device is indicated by energy level 64, the output pulse formed in receiver 61 varies in pulse width or time duration as an inverse function of the bias pressure. Thus high bias pressure results in a short pulse width 72, an intermediate bias pressure results in an intermediate pulse width '73, and a low bias pressure results in a long pulse width 74. Thus the control pressure signal in receiver leg 61 which is applied to the control port of fuel valve 21 is a train of pneumatic pressure pulses having a repetition rate which is a function of engine speed, each pulse having a time duration which is a function of the reciprocal of the bias pressure. Thus the periodic pneumatic control signal provided by the pulse module has a repetition rate which varies with changes in engine speed, the time duration of the pulses varying inversely with changes in the bias pressure.

The bias pressure appearing in bias conduit 67 is provided by the bias signal generating subcircuit including fluid integrating capacitance or filter 76, second fluidic switching device 61, and proportional amplifier 42, the

subcircuit being connected for receiving a speed signal from chopper 38 and a pressure signal analogue of the flow rate of air inducted into the engine from venturi 14.

Second fluidic switching device 41 is generally similar to though not necessarily identical with the first switching device 39. Preferably second switching device 41 is a monostable fluidic gating device including a power nozzle 77, a first preferred receiver leg 78, a second alternate receiver leg 79, a control port 81, and an inhibitor port 82. Power nozzle 77 is connected to the source of signal energy 30 by means of conduits 31 and 36. Control port 81 is connected to branch conduits 49, 51 for receiving triggering reference signal 2a, while inhibit port 82 is connected to branch conduits 46 and 48 through a capacitive coupling 83 and an impedance 84. The pressure rise characteristics of the reference signal are modified by the capacitive coupling to provide an inhibit signal similar to wave form 2b. Thus secondary fluidic switching device 41 is also connected in a configuration known as a oneshot multivibrator and has an external bias connection 86 for modifying the pulse width of the output signal in alternate receiver leg 79. Thus the second fluidic switching device 41 is also connected as a variable pulse width multivibrator. The output signal in alternate receiver leg 79 is a train of pressure pulses having a repetition rate determined by the reference triggering signal in control port 81, each pulse having a time duration or pulse width inversely proportional to the signal pressure present in conduit 86. The train of pressure pulses in alternate receiver leg 79 can be considered as a series of positive pressure excursions somewhat similar to wave form 2d in FIG. 2.

The integrating or filtering capacitor 76 receives the train of pressure pulses from alternate receiver leg 79 and provides a filtered analogue bias pressure in bias conduit 67 corresponding to the quotient of the speed signal applied to port 81 and the signal pressure in conduit 86.

The signal pressure in conduit 86 is derived from a venturi signal related to the flow rate of air inducted into the engine by means of proportional amplifier 42. Proportional amplifier 42 includes a power nozzle 87, a pair of alternate receiver legs 88, 89, and a pair of opposed control ports 91, 92. Power nozzle 87 is connected to the source of signal energy 30 through conduits 31, 33 and 37. Control port 91 is also connected to the source of signal energy 30 through a trimming re sistance 93 and'a conduit 94. In general, the operation of proportional amplifier 42 is such that the flow from power nozzle 87 is split between receivers 88, 89 as a function of the pressure difference across control ports 91, 92. For example, if control port 92 is connected to a reference pressure such as atmospheric pressure and a pressure drop occurs in port 91, then the pressure in receiver leg 88 increases, or if the pressure increases in port 91, the pressure decreases in receiver 88. A characteristic performance curve for such an amplifier is shown in FIG. 4 where the horizontal input pressure represents pressure in control port 91 and the vertical output pressure represents pressure in receiver leg 88. Trimming resistance 93 is preferably selected in accordance with the characteristics of the amplifier and the pressure variations expected in conduit 96 so that the net signal variation in control port 91 occurs either in an asymptotic portion of the amplifier response characteristic or in a linear portion thereof. Asymptotic response occurs when the amplifier is operated near saturation. For example, if operation is desired on a 5 linear portion of the characteristic, a small negative going pressure change in control port 91 results in a larger positive going pressure change in receiver 88, the input and output pressures being related by a relatively constant proportionality factor. On the other hand, if operation is desired over the asymptotic portion of the response characteristic, a relatively large negative going pressure change in control port 91 results in a small positive going pressure change in receiver leg 88. A second order hyperbolic relationship exists between the input and output pressures in the asymptotic range. For limited ranges of pressures the hyperbolic and parabolic functions closely approximate each other such that, in the asymptotic range the output pressure in receiver 88 can be made to closely approximate the square root of pressure changes in control port 91. Thus alternative modes of operation of fluid amplifier 42 are provided.

Where it is desired to operate amplifier 42 in its asymptotic range, the resistors 98, 99 and conduits 191i, 192 and 193 can be eliminated and control port 92 is then connected directly to atmosphere providing atmospheric pressure Pa as a reference pressure. According to this mode of operation, control port 91 is connected by means of conduits 96, 97 to the throat of venturi 14 such that the pressure in port 91 is related to the venturi pressure Pv. Thus the pressure difference across control ports 91, 92 is related to Pa Pv which is a function of r Q where r represents density of air and Q represents the flow rate of air inducted to the engine through venturi M. For example, an increase in flow rate Q results in a negative going pressure change in the venturi throat related to (1) which can be represented as P F in FIG. 4. In the asymptotic range, the negative going pressure change P P results in a positive going pressure change in output leg 38 represented by P P which is approximately proportional to the square root of the input pressure change. Thus the ressure increase in receiver leg 88 corresponds to if? or Q, providing a pressure signal in conduit 86 which changes with the changes in the flow rate of air inducted into the engine. Inasmuch as asymptotic operation of amplifier 42 results in small pressure changes in receiver 88, it may be desirable to provide additional proportional amplification means between receiver 88 and conduit 86 for boosting the pressure to a usable signal level.

Where it is desired to operate amplifier 42 over a linear portion of its operating range, the control port 92 is connected to fluid resistances 98, 99 and conduits 191, M92, 163 as shown in FIG. 1, resistance 98 being a sharp edged quadratic orifice and resistance 99 being a laminar flow linear orifice. According to this mode of operation, a negative pressure Pv in the venturi throat results in a small flow of air from atmosphere Pa through quadratic orifice 98, conduit 101, linear orifice 99, and conduits 192 and 97. This small flow of air responds to Pa Pv which is related to the square of the flow rate of air inducted into the engine Q The pressure drop across the quadratic orifice 98 responds to V Pa Pv which in turn responds to V Q or 0.

Thus the pressure drop across laminar orifice 99 is related to Q and appears as a pressure difference across control ports 91, 92. An increase in flow rate Q can be represented by the negative going pressure change P P across the control ports 91, 92 which results in a large positive going pressure change P P in output receiver leg 88 which is proportional to the change in the flow rate Q.

In summary, the flow rate Q of air inducted into the engine manifold is indicated in the venturi throat as a negative pressure proportional to Q Proportional amplifier 42 provides a positive output pressure in receiver 88 proportional to Q. Second fluidic switching device 41 provides a signal in receiver 79 in the form of a train of pulses having a repetition rate N where N is a function of engine speed, and a pulse width related to 1/0. The volume 76 filters or integrates this train of pulses to provide a bias pressure in conduit 67 proportional to N/Q. First fluidic switching device 39 provides a train of pneumatic pressure pulses in receiver 61 having a repetition rate N and pulse width related to Q/N. Inasmuch as the control signal applied to fuel valve 21 includes both a function of engine speed and a function of the reciprocal of engine speed, the net metering effect of the signal is related to Q. When measured over a given time period, the total of the fuel pulses equals the fuel requirement as determined by the flow rate of air inducted in the same time period.

What is claimed is: l. A fuel system for an internal combustion engine including a source of fuel under pressure, a fuel valve connected to said fuel source arranged for admitting intermittent timed injections of fuel to said engine in response to a periodic pneumatic control signal, and control means connected to said fuel valve for providing said periodic pneumatic control signal comprising:

a source of pneumatic signal energy; reference signal means connected to said engine providing a train of pneumatic triggering pulses having a repetition rate related to engine speed;

bias signal means connected to said engine providing a pneumatic pressure signal related to a selected operating condition thereof; and

pneumatic control signal forming apparatus including a primary fluidic gate device having a power nozzle connected to said signal energy source, a first preferred receiver leg, a second alternate receiver leg connected to said fuel valve, a control port connected to said reference signal means, and an inhibitor port connected to said reference signal means through a fluid capacitance coupling providing a multivibrator configuration, said inhibitor port being connected to said bias signal means, said gate device providing said pneumatic control signal in said second receiver leg in the form of a train of intermittent pressure pulses having a time duration inversely related to said bias signal pressure and a repetition rate related to engine speed.

2. A fuel system according to claim 1 in which said bias signal means is connected to said engine for monitoring engine speed and the flow rate of inducted air, said bias signal means providing a bias pressure which is the analogue of N/Q where N equals engine revolutions per unit of time and Q equals volume of inducted air per unit of time, said primary gate device providing said pneumatic control signal in the form of a train of pressure pulses having the relationship N X Q/N, such that the quantity of fuel delivered in a finite time period is proportional to the quantity of air inducted in said time period.

3. A fuel system according to claim 1 in which said bias signal means includes a fluid capacitance filter, a second fluidic gate device and flow rate measuring means connected in an inlet passage of said engine providing a pneumatic pressure analogue of Q where Q represents the volume of air inducted into said engine per unit of time, said second fluidic gate device having a preferred receiver leg and an alternate receiver leg connected to said filter, a control port and an inhibitor port connected to said reference signal means in a multivibrator configuration, said inhibitor port being connected to said flow rate measuring means for receiving said analogue of Q pressure signal, said second gate device providing a train of pressure pulses in said alternate receiver having a time duration proportional to l/Q and a repetition rate N where N represents engine revolutions per unit of time, said fluid capacitance filter integrating said train of pulses providing a bias pressure signal corresponding to the analogue of N/Q, said primary gate device providing said pneumatic control signal in the form of a train of pressure pulses having the relationship N X QIN, such that the quantity of fuel delivered in a finite time period is proportional to the quantity of air inducted in said time period.

4. A fuel system according to claim 3 in which said flow rate measuring means includes a proportional amplifier and a venturi arranged for measuring the flow rate of air inducted into said engine, said proportional amplifier having receiver means connected to said inhibitor port of said second fluidic gate device and having control port means connected to the throat of said venturi, said proportional amplifier being biased for operation near saturation providing a positive going output pressure change in said receiver means in response to a negative going pressure change in said control port means, said pressure change in said receiver means being approximately proportional to the square root of said pressure change in said control port means.

5. A fuel system according to claim 3 in whichsaid flow rate measuring means includes a venturi arranged for measuring the flow rate of air inducted into said engine, a sharp edged orifice and a laminar restriction connected in series between atmosphere and the throat of said venturi, and a proportional amplifier biased for linear response, said proportional amplifier having receiver means connected to said inhibitor port of said second fiuidic gate device, and having control port means connected across said laminar restriction, said proportional amplifier providing pressure changes in said receiver means proportional to changes in the flow rate of air inducted into said engine. 

1. A fuel system for an internal combustion engine including a source of fuel under pressure, a fuel valve connected to said fuel source arranged for admitting intermittent timed injections of fuel to said engine in response to a periodic pneumatic control signal, and control means connected to said fuel valve for providing said periodic pneumatic control signal comprising: a source of pneumatic signal energy; reference signal means connected to said engine providing a train of pneumatic triggering pulses having a repetition rate related to engine speed; bias signal means connected to said engine providing a pneumatic pressure signal related to a selected operating condition thereof; and pneumatic control signal forming apparatus including a primary fluidic gate device having a power nozzle connected to said signal energy source, a first preferred receiver leg, a second alternate receiver leg connected to said fuel valve, a control port connected to said reference signal means, and an inhibitor port connected to said reference signal means through a fluid capacitance coupling providing a multivibrator configuration, said inhibitor port being connected to said bias signal means, said gate device providing said pneumatic control signal in said second receiver leg in the form of a train of intermittent pressure pulses having a time duration inversely related to said bias signal pressure and a repetition rate related to engine speed.
 2. A fuel system according to claim 1 in which said bias signal means is connected to said engine for monitoring engine speed and the flow rate of inducted air, said bias signal means providing a bias pressure which is the analogue of N/Q where N equals engine revolutions per unit of time and Q equals volume of inducted air per unit of time, said primary gate device providing said pneumatic control signal in the form of a train of pressure pulses having the relationship N X Q/N, such that the quantity of fuel delivered in a finite time period is proportional to the quantity of air inducted in said time period.
 3. A fuel system according to claim 1 in which said bias signal means includes a fluid capacitance filter, a second fluidic gate device and flow rate measuring means connected in an inlet passage of said engine providing a pneumatic pressure analogue of Q where Q represents the volume of air inducted into said engine per unit of time, said second fluidic gate device having a preferred receiver leg and an alternate receiver leg connected to said filter, a control port and an inhibitor port connected to said reference signal means in a multivibrator configuration, said inhibitor port being connected to said flow rate measuring means for receiving said analogue of Q pressure signal, said second gate device providing a train of pressure pulses in said alternate receiver having a time duration proportional to 1/Q and a repetition rate N where N represents engine revolutions per unit of time, said fluid capacitance filter integrating said train of pulses providing a bias pressure signal corresponding to the analogue of N/Q, said primary gate device providing said pneumatic control signal in the form of a train of pressure pulses having the relationship N X Q/N, such that the quantity of fuel delivered in a finite time period is proportional to the quantity of air inducted in said time period.
 4. A fuel system according to claim 3 in which said flow rate measuring means includes a proportional amplifier and a venturi arranged for measuring the flow rate of air inducted into said engine, said proportional amplifier having receiver means connected to said inhibitor port of said second fluidic gate device and having control port means connected to the throat of said venturi, said proportional amplifier being biased for operation near saturation providing a positive going output pressure change in said receiver means in response to a negative going pressure change in said control port means, said pressure change in said receiver means being approximately proportional to the square root of said pressure change in said control port means.
 5. A fuel system according to claim 3 in which said flow rate measuring means includes a venturi arranged for measuring the flow rate of air inducted into said engine, a sharp edged orifice and a laminar restriction connected in series between atmosphere and the throat of said venturi, and a proportional amplifier biased for linear response, said proportional amplifier having receiver means connected to said inhibitor port of said second fluidic gate device, and having control port means connected across said laminar restriction, said proportional amplifier providing pressure changes in said receiver means proportional to changes in the flow rate of air inducted into said engine. 